Was just sorting through this myself recently, trying to make sense of the holes in the floor pans. There were four of them typically, in 70 I believe they began to appear when the T/A's & AAR's with the side exhaust came out. Before that I think all rubber plugs were used? Hopefully someone will correct me if I'm wrong. My R/T was built right in with the T/A's as far as time frame and it has 4 metal plugs. The ones circled in red would be the metal ones.The ones circled in green I believe are also (smaller) metal and T/A or AAR only, other cars would get a rubber plug there. Picture is from a T/A.